1. Field of the Invention
The present invention relates to apparatus for electrically stimulating muscle activity and more particularly to an apparatus and method for functional electrical stimulation of preselected muscles for tensioning the muscles to improve strength. The invention further relates to an apparatus and method for stimulating muscles more efficiently according to muscle type and work history.
2. Background of the Invention
The use of electrical pulses or signals to induce muscle contractions and, thus, stimulate muscle movement or exercise is well known in the medical sciences. A variety of methods and apparatus for stimulating muscle movement have been developed especially for application in the area of locomotion for paralyzed limbs. Along this line, there have been a number of attempts to develop apparatus that will allow individuals suffering from paralysis or various neurological or muscular disorders to walk or motivate otherwise non-functional muscles in a controlled manner.
At the same time, it is known that electrical stimulation is useful for general exercise of otherwise functional muscles for improving muscle tone or strength. Many applications exist for a method of improving muscle strength or tone to counter atrophy from disuse that is secondary to trauma or associated indirectly with some type of incapacitation. This includes long term bed rest, long term joint immobility do to fractures or fatiguing illnesses, or other bodily injuries or illnesses that restrict muscular exercise and use for prolonged periods.
It is also fairly well understood that general muscle strength, condition, and tone has a significant impact on overall health which is often undermined by inadequate exercise. Electrical stimulation may serve as an adjunct, in an otherwise healthy patient, to self induced muscular exercise to improve muscle strength. This is especially important in special applications such as in sports medicine where specific muscle groups can be strengthened to decrease the impact of injuries or surgery when traditional exercise is not possible.
Examples of the devices and protocols that have been developed for use in muscle therapy, training, motivation, control, or exercise are disclosed in U.S. Pat. Nos. 4,165,750, 4,177,819, 4,492,233 and 4,569,352.
U.S. Pat. No. 4,165,750, issued to Aleev et al., teaches a basic muscle stimulation device for use in bioelectrically controlled muscle stimulation. The stimulation device utilizes an oscillator circuit for generating an electrical signal at a frequency which stimulates muscular activity in a patient. This patent also discloses the dependence of the lower and upper amplitude limits of stimulation signals on specific muscle types and patients.
U.S. Pat. No. 4,177,819, issued to Kofskey et al, discloses a microprocessor controlled stimulation circuit which generates bursts of 2000-3000 Hertz signals of 2-20 second duration at 2-50 second intervals. The stimulating waveform increases and decreases in amplitude at the beginning and end of pulse periods and can be interrupted by no-load/overload sensors. The circuitry employs microprocessor technology and digital electronics control elements along with analog power amplifiers to implement the desired pulse pattern.
U.S. Pat. No. 4,492,233 further illustrates the use of transformers and high voltage transistors to drive electrodes at high voltages on the order of 300 volts maximum from digital input signals.
Aside from the limited application to muscle movement of paralyzed or incapacitated patients, the stimulators of these patents employ fixed stimulation signal energies, that is, frequencies or pulse widths, during given treatment periods. Changes in stimulation parameters during exercise, if any, are limited to signal amplitude and duty cycle. In some protocols, as disclosed in Computer Controlled Walking in the Paralyzed Individual, by J. S. Petrofsky and C. A. Phillips, Journal of Neurological and Orthopedic Surgery, Vol. 4, No. 2, July 1983, the relative position of joint members associated with the muscles are detected in an attempt to correlate stimulation with muscle motion but the work output is not directly measured or accounted for.
However, the above approaches do not cause muscles to exert maximum tension over a prolonged period of time. To achieve the maximum muscle tension or work during a treatment regime requires knowledge of variations in muscle properties during stimulation. The prior approaches, even when utilizing position sensitive feedback systems, do not measure actual muscle properties to determine the control parameters which account for time and stimulation dependent changes. This leads to such effects as early onset of fatigue on one hand or insufficient stimulation on the other, either of which prevents full and useful exercise. Without a properly balanced tension on the muscle over a prolonged treatment cycle, the muscle is not receiving maximum benefit and the process is inefficient.
The above approaches to muscle stimulation also suffer from the drawback that in a patient operated mode, they do not prevent over-stimulation that can cause muscle or point damage. At the same time, there is no provision for insuring patient compliance in terms of length of treatment or minimum muscle work levels. The prior art apparatus, therefore, requires extensive monitoring by a physician or trained personnel to assure proper use.
What is needed is a method and apparatus for exercising muscles through the application of functional electrical stimulation which achieves a maximum muscle tension dependent upon the current state of the muscle operating properties and, therefore, increased muscle strength through induced exercise. It would desirable to have an electrical stimulation exercise device that automatically adjusts to muscle properties and exercising conditions to assure proper treatment protocol and improved safety.